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PubMed1990

Population coding of stimulus orientation by striate cortical cells.

I have examined the performance of a population coding model of visual orientation discrimination, similar to the population coding models proposed for the coding of limb movements. The orientation of the stimulus is not represented by a single unit but by an ensemble of broadly tuned units in a distributed way. Each unit is represented by a vector whose magnitude and direction correspond to the response magnitude and preferred orientation of the unit, respectively. The orientation of the population vector, i.e. the vector sum of the ensemble of units, is the signalled orientation on a particular trial. The accuracy of this population vector orientation coding was determined as a function of a number of parameters by computer simulation. I have shown that even with broadly orientation tuned units possessing considerable response variance, the accuracy of the orientation of the population vector can be as good as behaviorally measured just noticeable differences in orientation. The accuracy of the population code is shown to depend upon the number of units, the average response strength, the orientation band-width, response variability and the response covariance. The results of these simulations were also compared to predictions derived from psychophysical studies of orientation discrimination.

Animals↗
PubMed2006

The haptic reproduction of orientations in three-dimensional space.

This research studied the haptic perception of orientations in space rather than in a plane. It aimed at identifying the nature of the system of coordinate used to represent an orientation in space, when two parameters are necessary to code an orientation. Blindfolded participants inserted the tip of the index finger in a thimble mounted at the extremity of a haptic interface, explored the orientation of a "virtual rod" with to-and-fro movements and, after a short delay, reproduced the same orientation with the same fingertip in the absence of the virtual rod. Globally, the haptic reproduction of orientations was anisotropic. When the reproduction of orientations was carried out in the frontal plane, a classical oblique effect (lower performance for the diagonal orientations than for the vertical and horizontal orientations) occurred. When the reproduction of orientations was carried out in space, orientations seemed to be coded in a coordinate system based on the sagittal plane.

Adult↗
PubMed2000

The functional role of oriented spatial filters in the perception of mirror symmetry--psychophysics and modeling.

We investigated human sensitivity to vertical mirror symmetry in noise patterns filtered for narrow bands of variable orientations. Sensitivity is defined here as the amount of spatial phase randomization corresponding to 75% correct performance in a 2AFC detection task. In Experiment 1, sensitivity was found to be high for tests patterns of all orientations except those parallel to the axis of symmetry. This implies that corresponding mirror-orientations (e.g. -45 and +45 degrees ) are combined prior to symmetry detection. In Experiment 2, observers detected symmetry in tests of variable orientation in the presence of either non-symmetric or symmetric masks filtered for orientations either parallel or perpendicular to the axis. Observers were found to be primarily affected by masks of the same orientation as the test, thus suggesting that symmetry is computed separately in distinct mirror-orientation channels. In Experiment 3, observers detected a symmetric test of variable height and width embedded in random noise. Data revealed that mirror symmetry is computed over a spatial integration region (IR) that remains approximately constant in area but whose height-to-width aspect ratio changes from 20:1 to 2:1 as orientation is varied from parallel to perpendicular to the axis. We compare human data against that of an ideal observer to identify key factors that limit visual performance and discuss the implications for the functional architecture of symmetry perception. We also propose a multi-channel model of symmetry detection that combines the output of oriented spatial filters in a simple and physiologically plausible manner. Particular emphasis is placed on the notion that changes in the shape of the IR with orientation compensate for changes in information density and partially equate performance across orientations.

Humans↗
PubMed2002

Representation of orientation in the somatosensory system.

In this paper we discuss how orientation is represented and transformed in the somatosensory system. Information about stimulus orientation plays an important role in sensory processing. In touch it provides critical information about how stimuli are positioned on the hand, which is important for grasping and lifting objects. It also provides important information about tactile shape. Psychophysical studies show that humans have a high capacity to discriminate the orientation of shapes and gratings indented into the finger pad. Further, these studies demonstrate that orientation discrimination is a reliable and stable method for assessing tactile spatial acuity. Neurophysiological studies suggest that orientation information is processed by the slowly adapting type 1 (SA1) afferent system. While orientation is poorly represented in the responses of individual afferent fibers, it is well represented in the population response properties of peripheral SA1 afferents and in the responses of central neurons in the primary (S1) and secondary (S2) somatosensory cortex. In S2, neurons with orientation selective and orientation non-selective responses tend to have large receptive fields that span multiple pads on multiple digits. Neurons in S2 that are orientation selective have similar tuning functions on different finger pads. These neurons may provide position-invariant responses or may be responsible for integrating features across hands, which is important for haptic object recognition of large shapes from the hand. Neurophysiological studies in trained animals show that the responses of about 85% of the neurons in S2 are affected by the animals focus of attention and that attention to the orientation of a bar modifies both the mean firing rate (i.e. gain) of neurons encoding orientation information and the degree of synchronous firing between pairs of neurons.

Animals↗
PubMed1992

Visual segmentation of oriented textures by infants.

The infant's visual system contains orientation-sensitive mechanisms from the first weeks of life. Differences in texture orientation can serve as a basis for rapid preattentive localization and segmentation in adults. We tested whether infants could use their orientation-sensitive mechanisms in the same way, by forced-choice preferential looking, using displays of line segments oriented at 45 degrees in a rectangular patch and 135 degrees in the surrounding region. Performance was compared with that for displays of similar elements with uniform orientation but with the patch defined by luminance contrast. Infants of 14-18 weeks old showed consistent preference for both orientation- and contrast-defined patches, indicating the ability to segment the field by orientation. Infants of 8-12 weeks performed comparably to the older infants on contrast-based segmentation but did not show a statistically significant preference with orientation-based segmentation. In a second experiment, preference was also tested for a region of mixed orientation versus a region of uniform orientation. The 14-18-week-olds did not show this preference, suggesting that their preference for the discrepant texture patch genuinely reflected texture segmentation and not simply the presence of two different orientations on one side of the display. The results are discussed in terms of the possible maturation of intracortical connections subserving texture grouping and segmentation.

Aging↗
PubMed2004

Unconscious orientation processing.

Recent findings have shown that certain attributes of visual stimuli, like orientation, are registered in cortical areas when the stimulus is unresolvable or perceptually invisible; however, there is no evidence to show that complex forms of orientation processing (e.g., modulatory effects of orientation on the processing of other features) could occur in the absence of awareness. To address these questions, different psychophysical paradigms were designed in six experiments to probe unconscious orientation processing. First we demonstrated orientation-selective adaptation and color-contingent orientation adaptation for peripheral unresolvable Gabor patches. The next experiments showed the modulatory effects of perceptually indiscriminable orientations on apparent motion processing and attentional mechanisms. Finally we investigated disappearance patterns of unresolvable Gabor stimuli during motion-induced blindness (MIB). Abrupt changes in local unresolvable orientations truncated MIB; however, orientation-based grouping failed to affect the MIB pattern when the orientations were unresolvable. Overall results revealed that unresolvable orientations substantially influence perception at multiple levels.

Adaptation, Physiological↗
PubMedDate not supplied

Are primate lateral geniculate nucleus (LGN) cells really sensitive to orientation or direction?

There is considerable controversy over the existence of orientation and direction sensitivity in lateral geniculate nucleus (LGN) neurons. Claims for the existence of these properties often were based upon data from cells tested well beyond their peak spatial frequencies. The goals of the present study were to examine the degree of orientation and direction sensitivity of LGN cells when tested at their peak spatial and temporal frequencies and to compare the tuning properties of these subcortical neurons with those of visual cortex. For this investigation, we used conventional extracellular recording to study orientation and direction sensitivities of owl monkey LGN cells by stimulating cells with drifting sinusoidal gratings at peak temporal frequencies, peak or higher spatial frequencies, and moderate contrast. A total of 110 LGN cells (32 koniocellular cells, 34 magnocellular cells, and 44 parvocellular cells) with eccentricities ranging from 2.6 deg to 27.5 deg were examined. Using the peak spatial and temporal frequencies for each cell, 41.8% of the LGN cells were found to be sensitive to orientation and 19.1% were direction sensitive. The degree of bias for orientation and direction did not vary with eccentricity or with cell class. Orientation sensitivity did, however, increase, and in some cases orientation preferences changed, at higher spatial frequencies. Increasing spatial frequency had no consistent effect on direction sensitivity. Compared to cortical cell orientation tuning, the prevalence and strength of LGN cell orientation and direction sensitivity are weak. Nevertheless, the high percentage of LGN cells sensitive to orientation even at peak spatial and temporal frequencies reinforces the view that subcortical biases could, in combination with activity-dependent cortical mechanisms and/or cortical inhibitory mechanisms, account for the much narrower orientation and direction tuning seen in visual cortex.

Animals↗
PubMed2001

The noradrenergic alpha2 agonist clonidine modulates behavioural and neuroanatomical correlates of human attentional orienting and alerting.

We examined whether the known noradrenergic attenuation of the alerting effect (the beneficial effect of a warning cue) results from an underlying effect of noradrenaline on temporal orienting (orienting toward a particular moment in time). Following a within-subjects, counterbalanced design, 10 healthy human volunteers received placebo, 200 microg clonidine or 1 mg guanfacine (alpha2 agonists) in three separate testing sessions. Subjects were scanned by fMRI while performing attentional orienting tasks containing spatially informative, temporally informative, non-informative or no cues. The alerting effect primarily activated left-lateralized prefrontal, premotor and parietal regions. Clonidine, but not guanfacine, impaired behavioural measures of the alerting effect while attenuating activity in the left temporo-parietal junction. Replicating previous results, the temporal orienting task activated left parietal and frontal cortex, while parietal cortex was activated bilaterally during spatial orienting. Of these networks, clonidine, but not guanfacine, attenuated left prefrontal cortex and insula activity during temporal orienting and attenuated right superior parietal cortex activity during spatial orienting,. To complement these neuroanatomical changes, clonidine produced selective behavioural effects on both temporal and spatial orienting. The anatomical dissociation between the effects of clonidine during temporal orienting versus alerting suggests that noradrenergic modulation of the alerting effect does not result only from an underlying effect on temporal orienting. Furthermore, we have demonstrated lateralized neuroanatomical substrates for the noradrenergic modulation of human attentional orienting in the spatial and temporal domains.

Adolescent↗
PubMed2003

Heart rate responses of women aged 23-67 years during competitive orienteering.

OBJECTIVES: To compare the heart rate responses of women orienteers of different standards and to assess any relation between heart rate responses and age. METHODS: Eighteen competitive women orienteers completed the study. They were divided into two groups: eight national standard orienteers (ages 23-67 years); 10 club standard orienteers (ages 24-67 years). Each participant had her heart rate monitored during a race recognised by the British Orienteering Federation. Peak heart rate (HR(PEAK)), mean heart rate (HR(MEAN)), standard deviation of her heart rate during each orienteering race (HR(SD)), and mean change in heart rate at each control point (DeltaHR(CONTROL)) were identified. The data were analysed using analysis of covariance with age as a covariate. RESULTS: National standard orienteers displayed a lower within orienteering race standard deviation in heart rate (6 (2) v 12 (2) beats/min, p<0.001) and a lower DeltaHR(CONTROL) (5 (1) v 17 (4) beats/min, p<0.001). The mean heart rate during competition was higher in the national standard group (170 (11) v 158 (11) beats/min, p = 0.025). The HR(MEAN) for the national and club standard groups were 99 (8)% and 88 (9)% of their age predicted maximum heart rate (220-age) respectively. All orienteers aged >55 years (n = 4) recorded HR(MEAN) greater than their age predicted maximum. CONCLUSIONS: The heart rate responses indicate that national and club standard women orienteers of all ages participate in the sport at a vigorous intensity. The higher DeltaHR(CONTROL) of club standard orienteers is probably due to failing to plan ahead before arriving at the controls and this, coupled with slowing down to navigate or relocate when lost, produced a higher HR(SD).

Adult↗
PubMed2003

Kinematic rules for upper and lower arm contributions to grasp orientation.

The purpose of the current study was to investigate the contribution of upper and lower arm torsion to grasp orientation during a reaching and grasping movement. In particular, we examined how the visuomotor system deals with the conflicting demands of coordinating upper and lower arm torsion and maintaining Donders' Law of the upper arm (a behavioral restriction of the axes of arm rotation to a two-dimensional "surface"). In experiment 1, subjects reached out and grasped a target block that was presented in one of 19 orientations (5 degrees clockwise increments from horizontal to vertical) at one position in a vertical presentation board. In experiment 2, target blocks were presented in one of three orientations (horizontal, three-quarter, and vertical) at nine different positions in the presentation board. If reach and grasp commands control the proximal and distal arms separately, then one would only expect the lower arm to contribute to grasp orientations and that Donders' Law would hold for the upper arm-independent of grasp orientations. Instead, as the required grasp orientation increased from horizontal to vertical, there was a significant clockwise torsional rotation in the upper arm, which accounted for 9% of the final vertical grasp orientation, and the lower arm, which accounted for 42%. A linear relationship existed between the torsional rotations of the upper and lower arm, which indicates that the components of the arm rotate in coordination with one another. The location-dependent aspects of upper and lower arm torsion remained invariant, however, yielding consistently shaped Donders' "surfaces" (with different torsional offsets) for different grasp orientations. These observations suggest that the entire arm-hand system contributes to grasp orientation, and therefore, the reach/grasp distinction is not directly reflected in proximal-distal kinematics but is better reflected in the distinction between these coordinated orienting rules and the location-dependent kinematic rules for the upper arm that result in Donders' Law for one given grasp orientation.

Adult↗
PubMed2006

Restoration of acoustic orienting into a cortically deaf hemifield by reversible deactivation of the contralesional superior colliculus: the acoustic "Sprague Effect".

Removal of all contiguous visual cortical areas of one hemisphere results in a contralateral hemianopia. Subsequent deactivation of the contralesional superior colliculus (SC) nullifies the effects of the visual cortex ablation and restores visual orienting responses into the cortically blind hemifield. This deficit nullification has become known as the "Sprague Effect." Similarly, in the auditory system, unilateral ablation of auditory cortex results in severe sound localization deficits, as assessed by acoustic orienting, to stimuli in the contralateral hemifield. The purpose of this study was to examine whether auditory orienting responses can be restored into the impaired hemifield during deactivation of the contralesional SC. Three mature cats were trained to orient toward and approach an acoustic stimulus (broadband, white noise burst) that was presented centrally, or at one of 12 peripheral loci, spaced at 15 degrees intervals. After training, a cryoloop was chronically implanted over the dorsal surface of the right SC. During cooling of the cooling loop to temperatures sufficient to deactivate the superficial and intermediate layers (SZ, SGS, SO, SGI), auditory orienting responses were eliminated into the left (contracooled) hemifield while leaving acoustic orienting into the right (ipsicooled) hemifield unimpaired. This deficit was temperature-dependently graded from periphery to center. After the effectiveness of the SC cooling loop was verified, auditory cortex of the middle and posterior ectosylvian and anterior and posterior sylvian gyri was removed from the left hemisphere. As expected, the auditory cortex ablation resulted in a profound deficit in orienting to acoustic stimuli presented at any position in the right (contralesional) hemifield, while leaving acoustic orienting into the left (ipsilesional) hemifield unimpaired. The ablations of auditory cortex did not have any impact on a visual detection and orienting task. The additional deactivation of the contralesional SC to temperatures sufficient to cool the superficial and intermediate layers nullified the deficit caused by the auditory cortex ablation and acoustic orienting responses were restored into the right hemifield. This restoration was temperature-dependently graded from center to periphery. The deactivations were localized and confirmed with reduced uptake of radiolabeled 2-deoxyglucose. Therefore deactivation of the right superior colliculus after the ablation of the left auditory cortex yields a fundamentally different result from that identified during deactivation of the right superior colliculus before the removal of left auditory cortex in the same animal. Thus the "Sprague Effect" is not unique to a particular sensory system and deactivation of the contralesional SC can restore either visual or acoustic orienting responses into an impaired hemifield after cortical damage.

Acoustic Stimulation↗
PubMed2001

Integration of perspective and disparity cues in surface-orientation-selective neurons of area CIP.

We investigated the effects of linear perspective and binocular disparity, as monocular and binocular depth cues, respectively, on the response of surface-orientation-selective (SOS) neurons in the caudal part of the lateral bank of the intraparietal sulcus (area CIP). During the single-unit recording, monkeys were required to perform the delayed-matching-to-sample (successive same/different discrimination) of discriminating surface orientation in stereoscopic computer graphics. Of 211 visually responsive neurons, 66 were intensively tested using the solid-figure stereogram (SFS) of a square plate with both disparity and perspective cues (D+P condition), and 62 of these were identified as SOS neurons for responding selectively to the orientation of stimuli. All these neurons were further tested using a solid figure with perspective cues alone (P-only condition), and 58% (36/62) of these showed selective response to the orientation of the stimuli. Of the 62 SOS neurons, 35 neurons were also tested using SFS with disparity cues alone (D-only condition) in addition to the D+P and P-only conditions. We classified these 35 neurons into four groups by comparing the response selectivity under the P-only and D-only conditions. More than one-half of these (19/35) were sensitive to both perspective and disparity cues (DP neurons), and nearly one-third (11/35) of these were sensitive to disparity cues alone (D neurons), but a few (2/35) were sensitive to perspective cues alone (P neurons). The remaining (3/35) neurons exhibited orientation selectivity only when both cues were present. In DP neurons, the preferred orientation under the D+P condition was correlated to those under the D-only and P-only conditions, and the response magnitude under the D+P condition was greater than those under the D-only and P-only conditions, suggesting the integration of both cues for the perception of surface orientation. However, in these neurons, the orientation tuning sharpness under the D+P and D-only conditions was higher than that under the P-only condition, suggesting the dominance of disparity cues. After the single-unit recording experiments, muscimol was microinjected into the recording site to temporarily inactivate its function. In all three effective cases out of six microinjection experiments, discrimination of a three-dimensional (3D) surface orientation was impaired when disparity cues alone were present. In only one effective case, when a relatively large amount of muscimol was microinjected, discrimination of a 3D surface orientation was impaired even when both disparity and perspective cues were present. These results suggest that linear perspective is an important cue for representations of a 3D surface of SOS neurons in area CIP, although it is less effective than binocular disparity, and that both of these depth cues may be integrated in area CIP for the perception of surface orientation in depth.

Algorithms↗
PubMed2002

Orientation selectivity is reduced by monocular deprivation in combination with PKA inhibitors.

We have previously shown that the protein kinase A (PKA) inhibitor, 8-chloroadenosine-3',5'-monophosphorothioate (Rp-8-Cl-cAMPS), abolishes ocular dominance plasticity in the cat visual cortex. Here we investigate the effect of this inhibitor on orientation selectivity. The inhibitor reduces orientation selectivity in monocularly deprived animals but not in normal animals. In other words, PKA inhibitors by themselves do not affect orientation selectivity, nor does monocular deprivation by itself, but monocular deprivation in combination with a PKA inhibitor does affect orientation selectivity. This result is found for the receptive fields in both deprived and nondeprived eyes. Although there is a tendency for the orientation selectivity in the nondeprived eye to be higher than the orientation selectivity in the deprived eye, the orientation selectivity in both eyes is considerably less than normal. The result is striking in animals at 4 wk of age. The effect of the monocular deprivation on orientation selectivity is reduced at 6 wk of age and absent at 9 wk of age, while the effect on ocular dominance shifts is less changed in agreement with previous results showing that the critical period for orientation/direction selectivity ends earlier than the critical period for ocular dominance. We conclude that closure of one eye in combination with inhibition of PKA reduces orientation selectivity during the period that orientation selectivity is still mutable and that the reduction in orientation selectivity is transferred to the nondeprived eye.

Animals↗
PubMed2006

Orientation discrimination and contrast detection thresholds in migraine for cardinal and oblique angles.

PURPOSE: To determine whether orientation discrimination deficits in migraine, which have been found to depend on the spatial frequency of the stimulus, are due to precortical dysfunction or to abnormal patterns of orientation tuning at cortical loci. Further, to assess whether any cortical involvement is restricted to the striate cortex or whether higher cortical areas are also involved. Orientation-specific abnormalities would provide evidence of cortical dysfunction. METHODS: Orientation-discrimination and contrast-detection thresholds were assessed at cardinal (0 degrees) and oblique (45 degrees) orientations using explicit lines defined by Gabor patches. To test for extrastriate dysfunction, participants made orientation judgments using virtual lines defined by two widely spaced circles. Migraine history, migraine triggers, and pattern sensitivity were also assessed. Twenty migraineurs (10 with visual aura, 10 without) and 20 control participants were tested. RESULTS: Orientation-discrimination thresholds were lower for discriminations made about the cardinal axis than for discriminations made about the oblique axis, a well-documented phenomenon known as the oblique effect. Relative to the control group, the migraine group exhibited orientation-specific sensitivity losses on explicit and virtual judgments. Orientation-discrimination thresholds about the oblique axis were significantly elevated in the migraine group. In contrast, the migraine and control groups' detection thresholds did not differ. CONCLUSIONS: These findings reflect abnormal function of striate and extrastriate cortex in migraine. In addition, the discrimination data are consistent with wider orientation-tuning curves for orientation-sensitive cells in migraine, whereas the detection data suggest peak sensitivity does not differ between the groups.

Adult↗
PubMed2001

Detection of shape orientation depends on salient axes of symmetry and elongation: evidence from visual search.

Three experiments investigated the role of the global spatial structure of two-dimensional (2-D) shapes in terms of symmetry and elongation on visual search for shape orientation. Experiment 1 demonstrated the often reported orientation search asymmetry (i.e., a faster detection of a tilted target among vertical distractors than the reverse) for the global orientation of 2-D polygons that possess a salient, "principal" axis of symmetry or elongation. Moreover, the search asymmetry depended on the orientation of the principal axis, rather than on the orientation of local contours. Further exploration of this effect with polygons (Experiment 2) showed that the search asymmetry for global orientation occurred for shapes containing an axis of symmetry; elongation, on the other hand, did not seem to be crucial. Finally, Experiment 3 demonstrated orientation search asymmetries with shapes composed of curved rather than straight contours: Here, the search asymmetry occurred as a function of the orientation of both axes of symmetry and elongation. Overall, search for global orientation was less efficient than search for local orientation. The results suggest that the perception of the global orientation of shapes is mediated by axis-based descriptions in terms of perceptually salient axes of symmetry and elongation.

Attention↗
PubMed1996

Gravitaxis screened for physical mechanism using g-modulated cellular orientational behaviour.

Advanced methods of recording cellular orientation with respect to the gravity vector are yielding increasingly wellfounded data on gravitaxis. The present study introduces a quantitative method which allows us to predict the precision of orientational behaviour as a function of acceleration assuming static buoyancy as a hypothetical physical principle of gravitaxis. The precision of orientation is expressed by the orientation coefficient as derived from circular statistics. Orientation coefficients calculated from experimental data at various g-values are tested for fit with a sigmoidal orientation coefficient-g-transfer function including a proportionality factor k. Residual orientation values in the low-hypogravity range obey a reciprocal function between k and g. Intersection of this residual-g function with the orientation coefficient-g-relationship gives the minimal acceleration to generate cellular orientation. Those data which clearly diverge from the orientation coefficient-g-curve bear some probability that the observed gravitaxis was guided in part by a physiological mechanism of gravireception and active graviorientation. Data which fit the orientation coefficient-g-curve qualify as being in agreement with a mechanical basis of cellular gravitaxis. Examples from the literature are presented and discussed in the light of our scheme of gravitaxis screening.

Acceleration↗
PubMedDate not supplied

Modeling V1 neuronal responses to orientation disparity.

The contribution of interocular orientation differences to depth perception, at either the neuronal or the psychophysical level, is unclear. To understand the responses of binocular neurons to orientation disparity, we extended the energy model of Ohzawa et al. (1990) to incorporate binocular differences in receptive-field orientation. The responses of the model to grating stimuli with interocular orientation differences were examined, along with the responses to random dot stereograms (RDS) depicting slanted surfaces. The responses to combinations of stimulus orientations in the two eyes were left-right separable, which means there was no consistent response to the binocular orientation difference. All existing neuronal data concerning orientation disparity can be well described by this type of model (even a version with no disparity selectivity). The disparity sensitive model is nonetheless sensitive to changes in RDS slant, although it requires narrow orientation bandwidth to produce substantial modulation. The disparity-insensitive model shows no selectivity to slant in this stimulus. Several modifications to the model were attempted to improve its selectivity for orientation disparity and/or slant. A model built by summing several disparity-sensitive models showed left-right inseparable responses, responding maximally to a consistent orientation difference. Despite this property, the selectivity for slant in RDS stimuli was no better than the simple disparity-selective model. The range of models evaluated here demonstrate that interocular orientation differences are neither necessary nor sufficient for signaling slant. In contrast, within the framework of the energy model, positional disparity sensitivity appears to be both necessary and sufficient.

Animals↗
PubMed1993

The layout of iso-orientation domains in area 18 of cat visual cortex: optical imaging reveals a pinwheel-like organization.

In this study we used optical imaging based on activity-dependent intrinsic signals to determine the distribution of cells responding to gratings of various orientations moving in different directions in area 18 of cat visual cortex. To test directional-selective clustering of neurons, we compared cortical activity maps obtained by stimulation with two gratings of identical orientation but moving in opposite directions. We found those maps to be almost identical, suggesting that neurons are not notably clustered into directionality columns. We also compared activity maps obtained with gratings of different orientations. Each of the orientation maps was similar to the 2-deoxyglucose maps previously reported. Having compiled the information obtained from the different orientations into one "orientation preference map," we found, in contrast to earlier reports, that iso-orientation domains are not elongated parallel bands but are small patches organized in "pinwheels" around points that we refer to as "orientation centers." We furthermore show that the only locations at which orientation preference changes rapidly are these orientation centers and not lines or loops. In addition, this report clarifies that our observations on the functional architecture of cat area 18, although at first sight at variance with earlier observations, are actually fully consistent with them. We therefore propose that in cat visual cortex pinwheel-like patterns of orientation preference form an irregular mosaic of modular units with an average density of 1.2 pinwheels per square millimeter.

Animals↗